Dialysis involves the movement of blood through a dialyzer having a semi-permeable membrane. The water supply used to initially prepare the dialysate or used during or after dialysis may contain a significant amount of dissolved gas such as nitrogen, oxygen, or carbon dioxide. Carbon dioxide may be formed as part of the breakdown of urea as spent dialysate flows through the sorbent cartridge. Removal of dissolved and undissolved gases from dialysate in a dialysis system can be important because dissolved gases can come out of solution in the dialysate circuit and cause gas bubbles, which can interfere with the proper functioning of the dialysis system. Gas bubbles can interfere with the smooth pumping of the dialysate in the dialysate loop, interfere with sensors in the dialysate loop, and can present a dangerous condition for the patient if the gas bubbles cross the dialyzer membrane into the patient's blood stream, potentially causing an air embolism.
Several methods and apparatuses are known in the art for degassing dialysate. For example, a pressure regulating system for a hemodialysis machine utilizes a deaeration pump and a regulator in a deaeration loop for minimizing pressure and flow transients in a heated water supply. The deaeration loop comprises a pump, a deaeration pressure regulator, a deaerator, and a back pressure regulator. The pump produces a negative pressure in heated water entering the deaeration pressure regulator to circulate the water in the deaeration loop and to enhance removal of air from the water. The back pressure regulator controls the loop water pressure to a value less than the incoming water pressure and supplies water to the dialyzer system of the machine isolated from supply water pressure and flow variations.
In an artificial kidney, dialysate concentrates and heated water are fed separately by pumps in fixed proportions to a mixing venturi where the water and liquid are combined to form a dialysate solution. In order to remove from the dialysate solution a desired portion of air which has been introduced therein from the water, the heated water is passed through a positive displacement pump having a restricted orifice bypass line before the heated water arrives at the mixing venturi. This causes consolidation of the air from small to large bubbles which are removed by a bubble trap. The resulting deaerated solution is then advanced through a header to branch lines to dialyzers.
A known apparatus for exposing a fluid to a negative pressure, particularly for degassing liquid containing a gas, comprises a double acting piston/cylinder unit of which the cylinder is divided into two chambers by the piston, the volume of one chamber swept by the piston being lesser than that swept by the piston in the other chamber. An inlet for a fluid is made to said one chamber, a conduit connects the two chambers and an outlet is made from the other chamber. Valve means are associated with the conduits to permit controlled reciprocation of the piston within the cylinder and fluid passed from said one chamber to the other is exposed to a negative pressure in the other chamber. In the situation in which the fluid is a gas-containing liquid, this negative pressure results in the formation of bubbles in the other chamber; alternatively, where the fluid is wholly liquid, a part of that liquid is vaporized. The contents of the other chamber are then passed through the outlet from the other chamber to, where the fluid is a gas-containing liquid, a bubble trap in which the gas is separated from the liquid or, where the fluid is wholly liquid, the gaseous phase or vapor will be condensed upon release of pressure and moved through the outlet to be used as required. In a variation, the piston/cylinder structure is replaced by a simple receptacle provided with a flexible diaphragm.
The known systems and methods cannot actively control a degassing process in order to selectively control a specific dissolved gas concentration within a desired range Instead, the systems described allow for general air removal from dialysate.
Hence, there is a need for a degassing system that can remove unwanted dissolved and undissolved gases from fluid before, during and after dialysis therapy. There is a need for a degassing system having the small size and weight necessary for a portable dialysis system. There is also a need for a degassing membrane that can allow a high degree of control over specific gas levels in dialysate. There is further a need for a degassing device that can function to remove specific gases with particularity from closed circuit dialysis systems.